This section provides background information related to the present disclosure and is not necessarily prior art.
In wireless communication, the upward access channel is the common shared channel and each terminal device may initiate an access procedure on the channel of its will. Therefore, if two or more terminals transmit access information concurrently, signals at the air interface may be mixed up. This will cause the receiver incapable of demodulating the signals from each transmitter, which is referred to as random access collision.
The method for random access is a procedure where access is initiated in the form of access probes. To reduce collision, orthogonal codes may be used to modulate the contents of the access probes. Different terminals may use different orthogonal codes to perform modulation for random access. In this way, the random access messages can be correctly received by the receiver even if the access probes are transmitted concurrently. However, in the scenario where different terminals simultaneously use the same orthogonal code to perform modulation, interference with one another may occur and the receiver may not be able to extract the useful information. Accordingly, in order to improve the performance of random access, it is necessary that the terminals avoid selecting the same orthogonal code at the same time of transmission.
In wireless communication, the reasons that the random access initiated by the terminal can be represented by different values. There are two primary types: paging response and initial call originated by the terminal. Paging refers to that a remote terminal calls a terminal in the wireless communication system. The terminal in the wireless communication system is known as a called party. Since the link from the remote side to the network has already been setup, the requirement for access latency is more demanding than that of the terminals, in the same condition, which originate the call. According to the different reasons for which the terminal initiates the random access, the conflicts as a result of utilizing the same orthogonal code by different terminals may be categorized into the conflicts between terminals which respond to the paging, the conflicts between the terminals which respond to the paging and the terminals which originate the call, and the conflicts between terminals which originate the call.
There are various ways to generate an orthogonal code, such as Walsh sequence, Golay sequence, etc. Walsh code is a code sequence consisting of 0, 1 or 1, −1 with its code length of 2n. Once the dimension of the Walsh code is determined, each combination of the Walsh codes can be determined. For instance, Walsh code of 1024 dimensions has 1024 different types of code sequences. Each sequence is 1024 bits in length, which may be referred to as 1024 code sequences. Every two code sequences are orthogonal to each other.
The random access with respect to the existing IEEE 802.20 protocol utilizes Walsh code with 1024 dimensions to modulate the contents of the access probes. Index number for 1024 code sequences is numbered as 0-1023, wherein index numbers 0-17 are reserved for the activation group for the purpose of handoff, power control and time correction. Index numbers 18-1023 (1006 in total) are reserved for the access terminal (AT) for transmitting access probes. The access terminal shall select a Walsh code using a uniform probability distribution over the 1006 index numbers no matter the access reason is to response a paging or to originate a call.
Paging is implemented using the downlink physical channel which is made up of several superframes. Each superframe includes a preamble at the beginning of the superframe and 24 physical frames, as illustrated in FIG. 1 and FIG. 2. FIG. 1 is the structure of a superframe specified by the existing IEEE 802.20 protocol. FIG. 2 is a schematic diagram of paging transmission and random access. It can be seen from the figures that every two superframes may transmit a quick paging block in the preamble of the first superframe. In the case where there is only one paging message, the quick paging block may include the entire content of the paging message, which may also be referred to as one step paging. In the case where the paging block includes 2 to 8 paging messages (8 paging messages at most), a complete paging message will be transmitted in the forward dedicated channel F-DCH on the frames which have physical frame numbers 1-7 of the superframe after the superframe where the quick paging block was sent. Such case may be referred to as a two-step paging. On the uplink physical channel, every superframe has 4 physical frames, with equal length, allowed to transmit random access probes, as illustrated in FIG. 1.
The content of the paging massage in the F-DCH is illustrated in FIG. 3. The field of the number of terminal ID, NumATIRecords, is 5 bits in length, indicating the number of paging messages of the terminals in the message. The times of the occurrences of two fields appeared later on, i.e., the terminal identifiers ATIRecords and the OpenConnectionRequired indicating whether a connection needs to be setup, is the value of parameters NumATIRecords. That is, the number of paging messages of the terminals refers to how many times these two fields have appeared. The number is ordered in sequence.
The paging message may also be transmitted to the terminal via paging message PageUATI in the F-DCH, as shown in FIG. 4. Paging to a terminal can be completed in this message. Such paging message may be a broadcasting message which can be received by all the terminals and the UATI field, and terminal unicast identifier in the message will be matched with the UATI preserved in the terminal.
According to the prior art, orthogonal codes are selected based on algorithms by all the terminals which intend to initiate random accesses. Therefore, it can hardly be prevented that the terminals, when responding to the paging, may select the same orthogonal code that the other terminals may select during an initiation for the call may. Moreover, it can hardly be prevented that the terminal, when responding to the paging, may select the same orthogonal code that the other terminals may select when responding to the paging. FIG. 5 is a schematic diagram illustrating the collision between different terminals which respond to the paging at the same time and the collision between the terminal which responds to the paging and the terminal which originates the call at the same time. As such, the terminal which responds to the paging may need several times of transmission of the probe until accessing into a system, which thereby extends the latency in the response to the paging and impacts the paging performance.